The present invention relates to a hydraulic shock absorber of damping force adjusting type mounted to a suspension of a motor vehicle and the like.
Among hydraulic shock absorbers, there is a hydraulic shock absorber of damping force adjusting type in which a damping force can properly be adjusted to enhance riding comfort and steering stability in dependence upon a road condition and/or a running condition.
Generally, in the hydraulic shock absorber of damping force adjusting type, a cylinder containing oil therein is divided into two chambers by a piston slidably mounted within the cylinder and connected to a piston rod, and a main oil passage and a bypass passage are formed in the piston to communicate the two cylinder chambers with each other. The main oil passage is provided with a damping force generating mechanism comprised of an orifice and a disc valve, and the bypass passage is provided with a damping force adjusting valve for adjusting a flow area of the bypass passage. One of the cylinder chambers is connected, through a base valve, to a reservoir for compensating for changes in the volume of the cylinder (caused by extension and retraction of the piston rod) by compression and expansion of gas.
With this arrangement, when the bypass passage is opened by opening the damping force adjusting valve, oil flow resistance between two cylinder chambers is reduced to decrease the damping force, and, when the bypass passage is closed to increase the oil flow resistance between two cylinder chambers, the damping force is increased. In this way, the damping force can be properly adjusted.
Among the damping force adjusting hydraulic shock absorbers of this kind, there is a shock absorber of damping force adjusting type in which a valve body of the damping force adjusting valve is driven by a proportional solenoid to adjust the damping force in accordance with current applied to a coil of the solenoid. In this damping force adjusting hydraulic shock absorber, in order to make the entire absorber compact, generally, a plunger of the proportional solenoid serves as the valve body and a fixed iron core of the proportional solenoid serves as a valve seat member. The bypass passage is provided with two ports, one of which is formed in the valve body and the other of which is formed in the valve seat member for slidably guiding the valve body, so that, when the valve body is reciprocally shifted in accordance with the current applied to the coil of the proportional solenoid, the valve body is shifted relative to the valve seat member to adjust the oil flow resistance of the bypass passage formed by the ports, thereby adjusting the damping force properly.
In the above-mentioned conventional technique, there arose a problem that displacement of the valve body is not proportional to the change in the damping force correctly.